Well I think one thing that definitely could have benefited your side gman would be targettable bait in a few categories. For instance, the majority of your chaff was cold resistant, so all the cold bolts were being targeted towards your mages. Similar for demons, because of the bells of cleansing. (The storm demons acted as bait a few times for those, but I don't think that was the intent.) So you need some fat (I.E. more HP than your mages) targets that are as vulnerable to crap as your mages (I.E. not cold resistant + demons) are positioned in front of them and grouped. It'd be nice if some experts could weigh in on how spell targeting is done for such things.
Lets see what else..... obviously, gman, you need to find some means of getting a water mage on the field for winter ward. Erm... both of you could possibly benefit from some attack rear cavalry or such on the flanks. In gman's case, just posting a grouping of units on the top and bottom right-most corners set to attack closest might help? You have the number advantage and thus want a better concave.... even despite the frost aura. Neither of you were using flanking spells..... hmm... contact me if you maybe want to invest in some lantern shield.... admittedly they most screw with AI then exploiting flanks, but still, a summon-at-borders spell is a summon-at-borders spell.
I like gman's attempt to use lightning, due to its armor negation and such. Not that I have any experience in blood, but Rush of Strength seems like the spell to cast-- 4 extra strength would greatly help. Life for a life spam looks nice as well if you have blood 8, but its more of one of those things you don't want to cast early since it takes time for the good targets to get in front.
As for the decisions that led to battle... I more or less agree with the decision to attack. Maybe I would have thought about trying to pull an attack with a minimal number of commanders to lead the swarm... but I think it is important to attack before the numbers became large enough on both sides for the battle line to become flat. As I said, you want the concave. Regardless, the numbers were large enough to make pd a non-factor. Inversely, I agree with kepoo's decision to not attack (assuming he didn't), as the territory in question is a stretch of low non-military value and, given your 4 fort(2 cap) situation, defense and some time to refortify seems more important than conquering. Then again a part of me disagrees since I think the giant races in general favor mid-game wars over late-game wars, and thus should be aggressive at them moment (as I am-- aggressive starting the instant expansion ended, first with r'yleh for the water (a useful asset for maneuverability) and then TC (for the gems and the 'safe' positioning (neighbors of my TC holdings = Lanka = my neighbor anyways though other holdings. Hell, my TC holdings allow me a more aggressive attack path against Lanka(Wait a tick... my auto-correct just had me capitalize Lanka?) then my natural holdings, thus attacking TC didn't add vulnerabilities, and even meant that an attack on my native land was 'defended' by a threat on Lanka's near-capital region)).... so I think neifle's decision to defend was alright for now, but a resolution to the build up was definitely in the neifle's favor in the long run. Given a few more turns of build up I think eventually niefel should have attacked.... but dominion was important here as well, cold scales matter. So preaching in the mean time, and throwing up a temple probably helps, but ultimately I think r'yleh's dom holds that land (and, for that fact, r'yleh should have held that entire northern mountain pass since turn 9(I know r'yleh attacked that area once an hardly failed, I caught a Lanka vs. independents battle where the independents was literally 2 units.)), and since I think r'ylehs dom is cold (which it should be, r'yleh is supposed to go either heat3 or cold3 and given the list of opponents cold3 is preferable (arguably a toss up, since neifel likes cold, but Agartha being amphib and cold blooded outweighs that.).
Meanwhile, the diplomatic side of this whole game has sorta become an issue of Lanka+Pangaea+Agartha vs. R'yleh+Neifel+TC, and I think this is certainly a layout that does not favor neifel.... Keboo-- you should have done a lot of diplomacy during the turns when it was obvious you were going to kill Ermor. The obvious bit of this is Pangaea-- a nation that was occupied with a war that was going to end and leave him powerful and seeking a new goal. However, less obvious, is what I consider the important question: If you take <potential gains>/<risks>, who scores the highest? Lanka had that thin attack path-- a 3 province long, 1 province thin, corridor leading to you-- lot to gain, little to risk. Agartha, meanwhile, had a lot to risk, but was close to your capital. Pangaea was arguably 1 to 1, much at risk, but roughly the same to grab. So admittedly Agartha wins the 'who looks like they're going to win' category, but Lanka's lack of wars plus their desirable border situation should have raised alarms and led you to seeking diplomatic security. Similarly, Pangaea's soon-to-end war, large swaths of land, and even border situations should have warranted attention.
As for Lanka's situation diplomatically, the war makes sense after the earlier Niefel->Agartha attack happened. Being nearly entirely surrounded by Agartha makes an attack against Niefel an incredibly secure prospect, as it 'defends' against Agartha. Also, as noted above, the vulnerable bit of Lanka is that single path through the bit between mountains and ocean-- they don't have much they need to defend. Peace, meanwhile, is one of those options that was viable to a point: gaining land is important. Arguably there was the alternative of assaulting TC's southern lands, but it was more of a risk due to that border being closer to Lanka's capital, as well as leading to more vulnerable regions (2 instead of 1).
So, I more or less agree with the battle. As for the result.... I see it as a push. Pangaea has joined in and that leads to some complicated issues. I'd say it is definitely Keboo's time to jump to the diplomacy board-- there is a lot on the table here, things that could keep him relevant and whatnot. Lanka doesn't have such luxury, he is pretty much trapped in his diplomatic stance, and, for that fact, his tactical stance, given the nature of the border.
[Disclaimer: I am quite drunk. The above probably reflects said level of drunkenness. That aside, this is still only my 3rd game, so my thoughts should be suspect even if I were sober.]